This invention relates to polyketone polymer compositions. More particularly, this invention relates to polyketone polymer compositions containing a stabilizer acting against long term heat degradation during their end-use.
Polymers of carbon monoxide and ethylenically unsaturated compounds, generally referred to as polyketones or polyketone polymers, are well known in the art. The class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated compound are of particular interest among polyketone polymers. This class of polymers is disclosed in numerous patent documents, exemplified by U.S. Pat. No. 4,880,865 and U.S. Pat. No. 4,818,811.
Polyketone polymers have utility as "Engineering Thermoplastics", or "ETP's", for which stringent end-use requirements apply. Since these plastics are used in high temperature applications, there is a strong need for effective stabilization against long term heat degradation during end-use applications.
In EP-A-289077 and EP-A-326223 it was found that only a few narrowly defined phenolic compounds produce desired stabilization against long term heat degradation in polyketone polymers. EP-A-289077 shows that the classes comprising diphenolic compounds, i.e. phenolic compounds with two phenolic groups provide good stabilization against long term heat degradation. EP-A-326223 teaches that particular classes of triphenolic compounds also provide good stability against long term heat degradation.
It was further shown in EP-A-289077 as well as EP-A-326223 that a monophenolic and a tetraphenolic compound, which are commercial top stabilizers against long term heat degradation for other polymers, result in very disappointing stabilization activity in polyketone polymers. The monophenolic compound is octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propanoate, the tetraphenolic compound is pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydoxyphenyl)propanoate].
In "Kirk-Othmer, Encyclopaedia of Chemical Technology", third Edition, Volume 3, p. 133 it is taught that for high temperature applications polynuclear phenolic compounds are preferred over monophenolic compounds because of their lower sublimation rate. The sublimation rate of a compound is directly related to its molecular weight; the higher the molecular weight, the lower the sublimation rate. According to the common general knowledge a preference thus exists for the use of phenolic compounds having a relatively high molecular weight.
In U.S. Pat. No. 5,082,885 various phenolic compounds were described as having utility for the improvement of polyketone melt stability and high temperature heat stability. The stabilizers comprised one of the following moieties para to the hydroxyl group: hydrogen, hydroxy, lower alkoxy, alkyl of up to C.sub.18, phenyl, halophenyl, or dialkyl hydroxyphenyl. The patent provides no direction for the selection of a C.sub.3-15 organic group nor more particularly, such a group comprising a carboxylic acid, carboxylic ester, ether, or carboxylic amide moiety. Further, the patent is directed against such a selection because it shows the weak performance of compounds such as 2,6-di-t-butyl-4-methoxyphenol within the content of the testing protocol used (see, e.g., Table I).
The above findings correspond with the finding that 2,6-di-t-butyl-4-methylphenol, a low molecular weight monophenolic stabilizer, gives a low level of stability against long term heat degradation in polyketone polymers.
However, it has now surprisingly been found that good stability against long term heat degradation can be achieved in polyketone polymers by applying as stabilizer a monophenolic compound having a relatively low molecular weight, which belongs to a narrowly defined class. In addition, the resulting compositions show attractive melt stability, as well as attractive mechanical and physical properties.